CISA.MS.EXO.12.1: IP allow lists SHOULD NOT be created.

ID	CISA.MS.EXO.12.1
Severity	Medium
Suite	CISA SCuBA baselines
Product	Exchange Online
Related products	Defender
Feature	Anti-spam
Security area	Email and collaboration protection
Resource type	Tenant
User impact of fixing	Low
Effort to fix	Medium
Benchmark	CISA SCuBA Secure Configuration Baselines for Microsoft 365 ScubaGear main, 2026-10-11, MS.EXO.12.1 (SHOULD)
Framework controls	cisa-scuba:MS.EXO.12.1 nist-800-53-r5:AC-4 Information Flow Enforcement
MITRE ATT&CK	T1566, T1684.002
Reads from	Exchange Online

What this checks and how to fix it

IP allow lists SHOULD NOT be created.

Rationale: Messages sent from IP addresses on an allow list bypass important security mechanisms, including spam filtering and sender authentication checks. Avoiding use of IP allow lists prevents potential threats from circumventing security mechanisms.

Remediation action:

To modify the connection filters, follow the instructions found in Use the Microsoft 365 Defender portal to modify the default connection filter policy.

1. Sign in to Microsoft 365 Defender portal.
2. From the left-hand menu, find Email & collaboration and select Policies and Rules.
3. Select Threat Policies from the list of policy names.
4. Under Policies, select Anti-spam.
5. Select Connection filter policy (Default).
6. Click Edit connection filter policy.
7. Ensure no addresses are specified under Always allow messages from the following IP addresses or address range.

Related links

• Defender admin center - Anti-spam policies
• CISA 12 IP Allow Lists - MS.EXO.12.1v1
• CISA ScubaGear Rego Reference

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Mito check, based on CISA ScubaGear. Author: soulemike; contributors: merill. Open-source licences.